Method for receiving ack/nack signal in mobile communication system

ABSTRACT

A method for transmitting information of resources for use in transmission of ACK/NACK signals in a mobile communication system is disclosed. An example method for receiving ACK/NACK signals in a mobile communication system is also disclosed. When resources for transmission of data and resources for transmission of control information of the data are scheduled through virtual unit resources, the method identifies information of resources for receiving an ACK/NACK signal for transmission data mapped to information of at least one of a virtual unit resource allocated to the transmission data and a virtual unit resource allocated to control information of the transmission data, and receives the ACK/NACK signal for the transmission data through the information of resources for receiving the ACK/NACK signal.

TECHNICAL FIELD

The present disclosure relates to a mobile communication system, andmore particularly, to transmission and reception of an ACK/NACK signalto acknowledge the receipt of data in a mobile communication system,especially, to a method for transmitting information of resources to beused for transmission and reception of ACK/NACK signals.

BACKGROUND ART

In a multi-carrier communication system, a base station controls data tobe transmitted to each terminal through downlink and also controls datathat each terminal transmits to the base station through uplink. Thebase station transmits control information to each terminal in order tocontrol downlink/uplink data transmission. This control information istransmitted to the terminal through part of downlink resources.

The control of uplink/downlink data transmission at the base station canbe referred to as scheduling and control of limited wireless resourcesfor multiple terminals or services can be referred to as wirelessresource scheduling. Wireless resource scheduling can be performedthrough actual unit resources used for data transmission. In this case,unit resources for scheduling at the base station and physical unitresources used for actual data transmission can be considered identical.

FIG. 1 illustrates an example of use of wireless resources in amulti-carrier system.

It can be seen from FIG. 1 that wireless resources of uplink anddownlink, i.e., time-frequency resources, are used for datatransmission. It can also be seen that downlink wireless resources areused not only for transmission of data but also for transmission ofcontrol information for controlling the downlink/uplink datatransmission described above.

The terminal can receive downlink data by receiving control informationtransmitted from the base station through downlink wireless resourcesand obtaining information of wireless resources or the like of the datatransmitted to the terminal through downlink wireless resources. Theterminal can transmit uplink data by receiving control informationtransmitted from the base station through downlink wireless resourcesand obtaining information of wireless resources or the like of the datato be transmitted from the terminal to the base station through uplinkwireless resources. Although not illustrated in FIG. 1, each terminalcan also transmit control information through uplink wireless resourcesto notify the base station of its channel state, data receiving state,terminal state, etc.

Each receiving side of data can transmit an ACK/NACK signal for the datato notify the transmitting side whether or not the receiving side hasnormally received the data having been transmitted from a base stationto a terminal through downlink or transmitted from a terminal to a basestation through uplink.

More specifically, to increase the reliability of data communication,the receiving side transmits a positive acknowledgement (ACK) when thedata has been received normally and transmits a negative acknowledgement(NACK) when the data has not been received normally.

The ACK/NACK signal occupies physical frequency and time resources sinceit is transmitted through downlink or uplink. When the terminal hastransmitted an ACK/NACK signal through uplink in response to datatransmitted from the base station through downlink, the base stationneeds to know the position of a resource through which the terminal hastransmitted the ACK/NACK signal for the data. On the other hand, whenthe base station has transmitted an ACK/NACK signal, the terminal needsto know the position of a resource through which the ACK/NACK signal hasbeen transmitted.

DISCLOSURE Technical Problem

An object of the present disclosure devised in view of the abovecircumstances in the background art lies in providing a method fortransmitting an ACK/NACK signal to acknowledge the receipt of data in amobile communication system.

Another object of the present disclosure devised to solve the problemlies in providing a method for determining information of resources tobe used for ACK/NACK transmission.

A further object of the present disclosure devised to solve the problemlies in providing a method for providing information of resources to beused for ACK/NACK transmission in a mobile communication system.

Technical Solution

The object of the present invention can be achieved by providing amethod for receiving an ACK/NACK signal in a mobile communicationsystem, the method including receiving reference signal information anda resource block index corresponding to a resource block allocated fortransmission of data; identifying ACK/NACK resource information throughthe reference signal information and the resource block index; andreceiving an ACK/NACK signal for the data using the ACK/NACK resourceinformation.

The resource block index may be a lowest one among resource blockindexes for the data.

The reference signal information may be a cyclic shift value for aspecific sequence. Here, the specific sequence and a sequence cyclicallyshifted by the cyclic shift value may be orthogonal to each other orhave good cross-correlation characteristics.

The reference signal may be allocated (or selected) from a referencesignal set including a plurality of reference signals.

The number of resource blocks allocated to the data may be equal to orlarger than a rank value applied to the mobile communication system.

In another aspect of the present invention, provided herein is a methodfor receiving an ACK/NACK signal in a mobile communication system, themethod including identifying an ACK/NACK resource index of transmissiondata mapped to a resource block index allocated for transmission of acontrol channel of the transmission; and receiving an ACK/NACK signalfor data associated with the control channel using a resource blockcorresponding to the ACK/NACK resource index, wherein at least oneACK/NACK resource index is repeatedly mapped (or double-mapped) to aplurality of resource block indexes.

The ACK/NACK resource index may be repeatedly mapped to the plurality ofresource block indexes in units of specific ACK/NACK resource indexsets.

The ACK/NACK resource index in the specific ACK/NACK resource index setmay be repeatedly mapped to the plurality of resource block indexesusing a different mapping rule.

The ACK/NACK resource index in the specific ACK/NACK resource index setmay be repeatedly mapped so as to avoid collision of ACK/NACK resourcesused in actual transmission.

The resource block index may be a lowest one among resource blockindexes of resource blocks allocated to the control information.

In another aspect of the present invention, provided herein is a methodfor receiving an ACK/NACK signal in a mobile communication system, themethod including identifying an ACK/NACK resource index of transmissiondata mapped to a resource block index allocated to control informationof the transmission data; and receiving an ACK/NACK signal for thetransmission data using the ACK/NACK signal resource index, wherein thesame ACK/NACK resource index is repeatedly mapped to at least oneresource block index.

Preferably, a plurality of resource block indexes are mapped to the atleast one ACK/NACK index using a different mapping rule for each of theplurality of resource block indexes.

Advantageous Effects

According to the method for transmitting ACK/NACK signals in a mobilecommunication system described in the present disclosure, it is possibleto efficiently obtain information of resources of the ACK/NACK signals.It is also possible to more efficiently use resources for transmissionof ACK/NACK signals.

According to the method, it is also possible to easily allocateresources for transmission of ACK/NACK signals in a mobile communicationsystem. The amount of control information can also be reduced sinceseparate information of resources for transmission and reception ofACK/NACK signals is not transmitted.

It is also possible to easily extend resources for transmission ofACK/NACK signals in a communication system that employs a MIMOtechnique. In addition, it is possible to increase the reliability ofdata communication through ACK/NACK signals.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of use of wireless resources in amulti-carrier system.

FIG. 2 illustrates a method for determining ACK/NACK indexes accordingto an embodiment of the invention.

FIG. 3 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

FIG. 4 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

FIG. 5 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

FIG. 6 illustrates a method for determining ACK/NACK indexes using theordinal information of a virtual unit resource according to thisembodiment of the invention.

FIG. 7 illustrates resources when a MIMO technique is used.

FIG. 8 illustrates a general procedure in which each codeword istransmitted to a transmit antenna of a MIMO system in a multi-carriersystem to which the MIMO scheme is applied.

FIG. 9 illustrates an example where data corresponding to a codeword isconnected to a transmit antenna port in a multi-carrier system to whicha MIMO technique is applied.

FIG. 10 illustrates another example where data corresponding to acodeword is connected to a transmit antenna port in a multi-carriersystem to which a MIMO technique is applied.

FIG. 11 illustrates a method in which an offset index is additionallyused according to another embodiment of the invention.

FIG. 12 illustrates a method in which an offset index is additionallyused according to another embodiment of the invention.

FIG. 13 illustrates an example where this embodiment of the invention isundesirably applied.

FIG. 14 illustrates a method of additionally using an offset indexaccording to another embodiment of the invention.

FIG. 15 illustrates a method of additionally using an offset indexaccording to another embodiment of the invention.

FIG. 16 illustrates an example method for determining an ACK/NACK indexaccording to another embodiment of the invention.

FIG. 17 illustrates an example method for determining an ACK/NACK indexaccording to another embodiment of the invention.

MODE FOR INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

To allow multiple terminals to transmit/receive data using commonresources, a base station can determine wireless resources to be used byeach terminal and inform the user of the determined wireless resourcesthrough scheduling. Here, the base station can control resources forreception/transmission of data through logical resources which arereferred to as virtual unit resources. The virtual unit resources, whichare logical resources, are in one-to-one correspondence with physicalresources according to a specific rule.

The embodiments of the invention described below are characterized inthat the base station does not perform wireless resource schedulingusing actual unit resources used for data transmission and, instead,performs scheduling indirectly using virtual unit resources. In thiscase, a specific relation is established between virtual unit resourcesand actual physical unit resources used for scheduling at the basestation, and, if the base station schedules wireless resources based onthe virtual unit resources, then transmission data is mapped to actualphysical unit resources based on the scheduling so that the transmissiondata is transmitted to the receiving side through the mapped actualphysical unit resources.

As described above, since ACK/NACK signals are transmitted throughspecific resources in uplink/downlink as described above, the receivingside can transmit an ACK/NACK signal only when it knows resourcesthrough which the ACK/NACK signal is transmitted. The transmitting sidecan also associate an ACK/NACK signal with data transmitted inuplink/downlink only when it knows resources through which the ACK/NACKsignal is transmitted.

For example, to receive an ACK/NACK signal for transmission data (ortransmitted data), the transmitting side infers information of aresource(s) for receiving the ACK/NACK signal for the transmission datausing information of virtual unit resources allocated to thetransmission data or virtual unit resources allocated to controlinformation of the transmission data. The transmitting side can receivethe ACK/NACK signal for the transmission data using the information ofresources for receiving the ACK/NACK signal.

The receiving side transmits an ACK/NACK signal for received dataaccording to a similar method. Specifically, the receiving side caninfer information of resources for transmitting an ACK/NACK signal fortransmission data using information of virtual unit resources allocatedto the transmission data or virtual unit resources allocated to controlinformation of the transmission data and can transmit the ACK/NACKsignal for the transmission data using the information of resources fortransmitting the ACK/NACK signal.

In addition, a set of virtual unit resources can be allocated totransmission data or control information of the transmission data. Inthis case, the transmitting side can determine information of resourcesfor transmitting the ACK/NACK signal through a virtual unit resourceincluded in the virtual unit resource set and can receive the ACK/NACKsignal using the determined information.

In the following description, it is assumed that ACK/NACK signals aretransmitted through specific unit resources of uplink/downlink, andresource numbers are allocated to unit resources, through which theACK/NACK signals are transmitted, and the allocated resource numbers areused for the unit resources. Resource numbers allocated to unitresources through which ACK/NACK signals are transmitted inuplink/downlink are referred to as ACK/NACK indexes. In this case, thereceiving side, which is the base station or terminal, can transmit anACK/NACK signal for received data using an ACK/NACK index and thetransmitting side, which is the terminal or base station, can determinewhich data corresponds to the ACK/NACK signal received from thereceiving side.

First Embodiment

One example of the virtual unit resource is a Virtual Resource Block(VRB). The VRB is a virtual unit resource for data transmission. The VRBincludes multiple Resource Elements (REs). If it is assumed that anactual physical unit resource is a Physical Resource Block (PRB), thenumber of REs included in one VRB is equal to the number of REs includedin one PRB. In actual data transmission, one VRB can be mapped to onePRB or can be mapped to a partial region of multiple PRBs. The term“VRB” will naturally be used interchangeably with the term “PRB” whenone VRB is mapped to one PRB in the following description.

Scheduling of downlink data transmission from the base station to aspecific terminal or uplink data transmission from a specific terminalto the base station is performed through one or more VRBs in onesubframe. When the base station transmits downlink data to a specificterminal, the base station informs the terminal of a downlink VRBthrough which the base station will transmit the data. In addition, toallow a specific terminal to transmit uplink data, the base stationinforms the specific terminal of an uplink VRB through which theterminal can transmit the data.

This embodiment provides a method in which, for example, VRB informationis used for obtaining or transmitting information of a correct resourceposition through which the receiving side is to transmit an ACK/NACKsignal for received data in a multi-carrier system.

FIG. 2 illustrates a method for determining ACK/NACK indexes accordingto an embodiment of the invention.

A resource number allocated to a VRB or a VRB position will now bereferred to as a VRB index. According to this embodiment, when thetransmitting side transmits data by allocating it to one or more VRBs, arelation is established between a VRB index and an ACK/NACK index(es) toallow the receiving side to obtain information of resources fortransmitting/receiving an ACK/NACK signal for the transmitted data.

Specifically, FIG. 2 shows an example in which ACK/NACK indexes areallocated respectively to VRB indexes. The receiving side determines anACK/NACK index using a VRB index of a VRB allocated for datatransmission/reception. Using the determined ACK/NACK index, thereceiving side can obtain information of an ACK/NACK resource fortransmitting an ACK/NACK signal for received data.

As shown in FIG. 2, data of one terminal can be allocated to multipleVRBs through which the data can be transmitted. Transmission of oneACK/NACK signal is needed for single data. Therefore, when thetransmitting side transmits data by allocating it multiple VRBs, thereceiving side can select one of the respective VRB indexes of themultiple VRBs to which the data has been allocated and can transmit anACK/NACK signal using a resource corresponding to an ACK/NACK indexcorresponding to the selected VRB index. For example, when thetransmitting side transmits data by allocating it to multiple VRBs, thereceiving side can transmit an ACK/NACK signal for the transmitted datausing an ACK/NACK index corresponding to the smallest of the multipleVRBs.

Second Embodiment

Another example of the virtual unit resource is a Control ChannelElement (CCE).

When a plurality of control channel information are transmitted using nOFDM symbols in a subframe serving as a transmission time interval, eachCCE is transmitted by mapping to resource elements in the physicaldomain. A CCE is an entity constructed to transmit a plurality ofcontrol information of one terminal and the amount of controlinformation transmittable through a CCE can be defined by a predefinedcoding rate and modulation method. A plurality of control informationcan be transmitted through one or more CCEs in order to provide a codingrate for achieving a specific reception quality to a terminal when amodulation method has been defined.

When the base station transmits data through downlink or receives datafrom a terminal, the base station can transmit control information tothe terminal through one or more CCEs in order to notify the terminal ofadditional information of data/information or a resource position towhich the data/information has been allocated. Each CCE is mapped to aresource in the downlink time-frequency domain. The CCE can beconsidered a minimum resource unit of control information for datatransmission in each of downlink and uplink.

Using this control information, the terminal can determine, whenreceiving data from the base station, VRB resources used for receivingthe data and can determine, when transmitting data to the base station,VRB resources in uplink which can be used to transmit the data.

The CCE is a logical resource conceptually similar to the VRB.Therefore, even though single control information is transmitted througha set of consecutive CCEs, it can be transmitted through discontinuousresources in actual physical resources. The relation between theselogical/physical resources can be predefined in the system.

Different CCEs can be defined for control information for downlink dataand control information for uplink data. That is, an independent CCE canbe determined for each of uplink and downlink since the size of controlinformation for downlink can be different from the size of controlinformation for uplink.

In the case where data is transmitted through downlink, the base stationtransmits control information to a terminal, which will receive thedata, through a CCE or a set of CCEs to notify the terminal ofinformation of a VRB or a set of VRBs, through which the data istransmitted, and other additional control information. After receivingthis control information, the terminal receives the data and transmitsan ACK or NACK to the base station through uplink to acknowledge thereceipt of the data.

In the case where data is transmitted through uplink, the base stationtransmits control information through a CCE or a set of CCEs to notifythe terminal of information of uplink VRBs available to the terminal.After receiving this control information, the terminal transmits datausing the uplink VRB information. After receiving the data, the basestation transmits an ACK or NACK through downlink to notify the terminalwhether or not the base station has received the data.

This embodiment provides a method in which, for example, CCE informationis used for obtaining or transmitting information of a correct resourceposition through which the receiving side is to transmit an ACK/NACKsignal for received data in a multi-carrier system.

FIG. 3 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

A resource number allocated to a CCE or a CCE position will now bereferred to as a CCE index. According to this embodiment, when thetransmitting side transmits control information of transmission data byallocating the control information to one or more CCEs, a relation isestablished between a CCE index and an ACK/NACK index to allow thereceiving side to obtain information of resources for an ACK/NACK signalfor the transmitted data.

Specifically, FIG. 3 shows an example in which ACK/NACK indexes areallocated respectively to CCE indexes. The receiving side can obtain anACK/NACK index using a CCE index of a CCE allocated for controlinformation transmission/reception. Using the obtained ACK/NACK index,the receiving side can obtain information of an ACK/NACK resource fortransmitting an ACK/NACK signal for received data corresponding to thecontrol information.

As shown in FIG. 3, control information of one terminal or data can betransmitted by allocating the controlling information to multiple CCEs.Generally, control information is transmitted to terminals at variouslocations and a mixture of a plurality of control information allocatedto a set of CCEs is transmitted through downlink. However, when singlecontrol information is transmitted through a set of CCEs, one CCE indexis selected from multiple CCE indexes occupied by the controlinformation and an ACK/NACK signal is transmitted using an ACK/NACKindex corresponding to the selected CCE index. For example, an ACK/NACKsignal can be transmitted and received using an ACK/NACK indexcorresponding to the smallest of the CCE indexes occupied by the controlinformation.

In the embodiment of FIG. 3, the base station can transmit ACK/NACKsignals without collision of ACK/NACK resources since ACK/NACK indexes1, 4, 5, 8, 9, and 12 are used for downlink data and ACK/NACK indexes 3and 11 are used for uplink data.

FIG. 4 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

The amount (or number) of ACK/NACK resources that should be secured doesnot necessarily correspond to the number of CCE indexes since ACK/NACKsignals of uplink and downlink are transmitted separately. For example,if ACK/NACK resources are allocated in advance for ACK/NACK indexes inone-to-one correspondence with CCE indexes, not all allocated ACK/NACKresources will be used and will be wasted in most situations.

Thus, repeated use of ACK/NACK indexes corresponding to CCE indexes willenable more efficient operation of ACK/NACK resources. That is, oneACK/NACK index may be repeatedly allocated (or double-allocated) to aplurality of CCE indexes. Here, it is preferable that the ACK/NACK index(i.e., ACK/NACK resource) not be used as an ACK/NACK resource for othercontrol information.

As shown in FIG. 4, ACK/NACK indexes 1, 2, 3, and 4 mapped to CCEindexes 1, 2, 3, and 4 may be repeatedly used for CCE indexes 9, 10, 11,and 12. In the embodiment of FIG. 4, the base station can transmitACK/NACK signals without collision of ACK/NACK resources even thoughACK/NACK indexes are repeatedly used since ACK/NACK indexes 1, 4, 5, 8,2, and 3 are used for downlink data and ACK/NACK indexes 3 and 11 areused for uplink data.

Reference will now be made in more detail to an example of the methodfor repeatedly allocating ACK/NACK indexes (i.e., ACK/NACK resources).

FIG. 5 illustrates a method for determining ACK/NACK indexes accordingto another embodiment of the invention.

In this embodiment, ACK/NACK indexes mapped to information of aplurality of virtual unit resources included in a virtual unit resourceset, which includes a largest number of virtual unit resources, are usedas ACK/NACK indexes that are repeatedly mapped. Here, it is preferablethat different mapping rules be applied when the same ACK/NACK indexesare mapped to virtual unit resource sets.

ACK/NACK indexes mapped to control information included in the largestCCE set can be referred to as an ACK/NACK Index Group (ANIG). WhenACK/NACK indexes are repeatedly mapped to CCE indexes, they may bemapped on an ANIG basis (or in units of ANIGs). Here, it is preferablethat ACK/NACK indexes in an ANIG be repeatedly mapped in a differentcorrespondence when ACK/NACK indexes in an ANIG are repeatedly mapped toCCEs. That is, when ACK/NACK indexes are mapped to CCE indexes on alargest CCE set basis (or in units of the largest CCE set), ACK/NACKindexes in an ANIG mapped to a set of CCE indexes can be remapped to adifferent set of CCE indexes in a different mapping order.

If ACK/NACK indexes mapped to a set of CCE indexes are remapped to adifferent set of CCE indexes in a different mapping order in thismanner, it is possible to more efficiently allocate ACK/NACK resourcesusing CCE indexes when one or more control information are transmittedthrough CCEs.

As shown in FIG. 5, when it is assumed that the largest CCE set is a CCEset including four CCE indexes 1, 2, 3, and 4, ACK/NACK indexes (1, 2,3, 4) are mapped to CCE indexes (1, 2, 3, 4) and CCE indexes (9, 10, 11,12). However, ACK/NACK indexes (2, 1, 4, 3), which are ordereddifferently from (1, 2, 3, 4), are mapped to CCE indexes (9, 10, 11,12).

While 12 ACK/NACK resources are necessary when different ACK/NACKindexes are allocated to all CCEs, ACK/NACK signals can be transmittedin each link using only 8 ACK/NACK resources if ACK/NACK indexes (1, 2,3, 4) are repeatedly mapped to CCE indexes according to the method shownin FIG. 5.

In addition, information of resources for receiving uplink ACK/NACKsignals and information of resources for receiving downlink ACK/NACKsignals can be mapped separately from each other. The setting ofACK/NACK indexes illustrated in FIG. 5 can be considered a setting foreither uplink or downlink. That is, an uplink ACK/NACK index and adownlink ACK/NACK index can be separately set for the same CCE as shownin FIG. 5.

Although a large number of CCEs can be actually transmitted in amulti-carrier system, the number of a plurality of control informationthat can be transmitted is not necessarily equal to the number of CCEssince the overall throughput of the system is not significantly reducedeven if the number of a plurality of control information that can betransmitted at once is limited in the system. Accordingly, the number ofACK/NACK resources that are allocated may be different from the numberof CCEs that can be transmitted in the multi-carrier system and may beequal to the number of a plurality of control information that aretransmitted at once.

Third Embodiment

Reference will now be made to a method in which the ordinal informationof a virtual unit resource of transmission data or control informationof the transmission data in a single subframe is used as ACK/NACKresource information according to another embodiment of the invention.

In an example of this method, the ordinal number of a VRB, containingdata of a corresponding terminal, in VRBs in a subframe is associatedwith an ACK/NACK index. Accordingly, the terminal can obtain an ACK/NACKindex by determining the ordinal number of data (or control information)among a plurality of transmitted data using a VRB through which the datais transmitted.

In another example of the method, the ordinal number of controlinformation among CCEs in a subframe may be associated with an ACK/NACKindex. That is, when control information for uplink/downlink datatransmission/reception is transmitted to a terminal, the terminal canobtain an ACK/NACK index by determining the ordinal number of thecontrol information transmitted to the terminal among alluplink/downlink control information.

To efficiently implement this embodiment, it is preferable that the basestation and the terminal share the number of a plurality of controlinformation that the base station can transmit in a subframe and theplurality of control information be arranged in order of decreasing orincreasing amount (or number) of CCE resources occupied by the controlinformation.

FIG. 6 illustrates a method for determining ACK/NACK indexes using theordinal information of a virtual unit resource according to thisembodiment of the invention.

A description will now be given of a method in which the ordinalinformation of a virtual unit resource of transmission data or controlinformation of the transmission data in a single subframe is used asACK/NACK resource information according to this embodiment of theinvention.

In an example of this method, the ordinal number of a VRB, containingdata of a corresponding terminal, in VRBs in a subframe is associatedwith an ACK/NACK index. Accordingly, the terminal can obtain an ACK/NACKindex by determining the ordinal number of data (or control information)among a plurality of transmitted data using a VRB through which the datais transmitted.

In another example of the method, the ordinal number of controlinformation among CCEs in a subframe may be associated with an ACK/NACKindex. That is, when control information for uplink/downlink datatransmission/reception is transmitted to a terminal, the terminal canobtain an ACK/NACK index by determining the ordinal number of thecontrol information transmitted to the terminal among alluplink/downlink control information.

To efficiently implement this embodiment, it is preferable that the basestation and the terminal share the number of a plurality of controlinformation that the base station can transmit in a subframe and theplurality of control information be arranged in order of decreasing orincreasing amount (or number) of CCE resources occupied by the controlinformation.

FIG. 6 shows an example of the allocation of ACK/NACK indexes to CCEsand the association between the ACK/NACK indexes and the allocated CCEswhen 12 CCEs are present in downlink while the number of controlinformation transmitted in a time interval occupying 4 CCEs is 1, thenumber of control information occupying 2 CCEs is 3, and the number ofcontrol information occupying one CCE is 1. In this example, theplurality of control information are arranged in order of decreasingamount of CCE resources occupied by the control information.

In the embodiment of FIG. 6, a first terminal receives controlinformation having a size of two CCEs corresponding to CCE indexes 9 and10. The first terminal already knows that a plurality of controlinformation has been transmitted in order of decreasing size of controlinformation and that the plurality of control information includes onecontrol information of a size of four CCEs and three control informationof a size of two CCEs. Accordingly, the first terminal can determinethat the received control information is the fourth of the total of 5control information transmitted. As a result, the first terminal candetermine that transmission of an ACK/NACK signal for data controlled bythe received control information uses an ACK/NACK resource correspondingto a fourth ACK/NACK index.

Fourth Embodiment

Reference will now be made to a method in which ACK/NACK resourceinformation is transmitted by incorporation into transmission data orcontrol information of the transmission data.

In this method, when a base station transmits control information fortransmission and reception of data to a terminal, information indicatingan ACK/NACK index used by the data is included in the data or thecontrol information. For example, N_(AN) bits may be added to controlinformation to indicate an ACK/NACK index of the correspondingdata/information. Using this method, the base station can directlycontrol ACK/NACK resources used by all data. Accordingly, the basestation can flexibly change the amount of resources to be used forACK/NACK transmission according to circumstances.

FIG. 7 illustrates resources when a MIMO technique is used.

When the MIMO technique is applied, it is possible to transmit datausing diversity in the spatial domain in the same frequency and timeresources. That is, the same time-frequency resources are shared bydifferent data. Generally, a system which uses the MIMO technique uses aspatial multiplexing technique which is referred to as precoding.

When data is transmitted in a MIMO system, a data information block isconverted into a decoded codeword. Therefore, one codeword can beconsidered one data information block. This codeword corresponds to avirtual antenna layer, and the antenna layer is associated with anactual transmit antenna port through precoding.

FIG. 8 illustrates a general procedure in which each codeword istransmitted to a transmit antenna of a MIMO system in a multi-carriersystem to which the MIMO scheme is applied.

As shown in FIG. 8, each codeword 80 generally corresponds to a specificlayer 82 through a codeword-layer mapping module 81 in a MIMOmulti-carrier system. The number of codewords N_(C) may not be equal tothe number of layers N_(L). How each codeword is mapped to a layerdepends on which precoding matrix is used for precoding. The number oflayers can be referred to as a rank.

Although ranks may not be equal in a total frequency band, generally,all frequency regions of data transmitted to a specific terminal indownlink have the same rank value and all frequency regions of datatransmitted by the terminal in uplink also use the same rank value. Indownlink, the rank value used in a total frequency band maysignificantly vary since the base station transmits data to multipleterminals in downlink.

A precoding module 83 for performing precoding can be represented by aN_(T)×N_(L) precoding matrix which is represented by N_(T) columnvectors having a length of N_(L). Consequently, a layer to which eachcodeword is mapped can be determined according to one or more precodingcolumn vectors which the codeword uses.

FIG. 9 illustrates an example where data corresponding to a codeword isconnected to a transmit antenna port in a multi-carrier system to whicha MIMO technique is applied. FIG. 10 illustrates another example wheredata corresponding to a codeword is connected to a transmit antenna portin a multi-carrier system to which a MIMO technique is applied.

When the MIMO technique is applied to the multi-carrier system, it ispossible to efficiently increase spatial resources in proportion to therank according to the MIMO technique in frequency and time resources.This also has an advantage in that the amount of data transmitted isincreased in proportion to the rank. However, this also increases theamount of corresponding ACK/NACK resources. That is, ACK/NACK signals,which are increased in number as the amount of data increases since thedata is transmitted according to the MIMO technique, must be transmittedin the opposite link. However, increasing the amount of requiredACK/NACK resources may reduce the efficiency of the multi-carrier systemsince ACK/NACK signals are not necessarily transmitted using the MIMOtechnique.

In the MIMO-based system, the number of ACK/NACK indexes which can bemapped through VRBs or CCEs may be more limited than the number oftransmittable data. For example, it is assumed that VRB indexes andACK/NACK indexes are mapped using the method described in the firstembodiment. Even when the same time-frequency resources are used in theMIMO system, two or more codewords can be transmitted if spatialresources are divided and used. However, since VRB indexes are mapped toACK/NACK indexes, the number of expressible ACK/NACK indexes is lessthan the number of transmittable data. This may also be true when amethod, where CCE indexes are mapped to ACK/NACK indexes, is used.

In addition, a plurality of codewords can be transmitted in a systemwhich uses the MIMO technique as described above. Here, the number ofcodewords transmitted through the same time-frequency resources may varydepending on wireless channel environments. Accordingly, the associationof ACK/NACK resources when multiple codewords are transmitted and whenone codeword is transmitted may become indefinite.

The following embodiments suggest methods in which a terminal can obtainan ACK/NACK index which is a unique number of an ACK/NACK resourcethrough which an ACK/NACK signal is transmitted and received in a systemusing a MIMO technique. The methods according to the embodiments willnot necessarily be used in a MIMO system.

Fifth Embodiment

According to this embodiment, an ACK/NACK index of transmission data canbe mapped to a combination of information of a virtual unit resourceallocated to the transmission data or a virtual unit resource allocatedto control information of the transmission data and additionalinformation. For example, the number of possible ACK/NACK indexes when aMIMO technique is applied to the multi-carrier communication system maybe less than the number of transmittable data. By incorporatingadditional information, it is possible to increase the limited number ofACK/NACK indexes that can be mapped through VRBs or CCEs.

The following is a method for determining ACK/NACK indexes according tothis embodiment. In the above embodiments where no MIMO is considered,an ACK/NACK index is transmitted by mapping to virtual unit resourceinformation, for example a VRB index or a CCE index. This embodimentdescribed below provides a method in which an offset index is used asadditional information. That is, an ACK/NACK index can be obtained usinga combination of a VRB index or CCE index and an offset index.

In this case, information of an offset index can be provided to aterminal when a base station transmits multiple codewords. The offsetindex information may also be provided using information shared by boththe base station and the terminal without transmission of additionalinformation. The offset index information may also be predefined in thesystem. The offset index value may be negative.

Equations 1 and 2 show example methods in which ACK/NACK indexes aredetermined by combining VRB indexes and CCE indexes with offset indexes,respectively.

I _(ACK/NACK) =I _(offset) +I _(VRB) , I _(VRB)=0,1,2, . . . ,N_(VRB-1)  EQUATION 1

I _(ACK/NACK) =I _(offset) +I _(CCE) , I _(CCE)=0,1,2, . . . ,N_(CCE-1)  EQUATION 2

“I_(VRB)” in Equation 1 denotes a VRB index and “I_(CCE)” in Equation 2denotes a CCE index. I_(VRB) and I_(CCE) may have an integer in theranges of 0 to N_(VRB-1) and N_(CCE-1), respectively. Here, N_(VRB)denotes the total number of indices I_(VRB) and N_(CCE) denotes thetotal number of indices I_(CCE). Especially, it is assumed that the VRBindex or CCE index is smallest when a number of VRBs or CCEs areallocated to single data or control information. In Equations 1 and 2,I_(offset) denotes an offset index and I_(ACK/NACK) denotes an ACK/NACKindex.

Here, it is assumed that the transmitting and receiving sides receiveinformation indicating that the according to the rules previously agreedupon therebetween. Then, I_(ACK/NACK) can be determined to be the sum ofI_(VRB) and I_(offset). Alternatively, I_(ACK/NACK) can be determined tobe the sum of I_(CCE) and I_(offset). FIGS. 11 and 12 illustrate amethod in which an offset index is additionally used according to anembodiment of the invention.

Examples of FIGS. 11 and 12 are described below together since thisembodiment is similarly applied to the examples of FIGS. 11 and 12 withthe only difference being that the two examples relate to uplink anddownlink transmission, respectively. In FIGS. 11 and 12, the horizontalaxis represents a Resource Block (RB) index and the vertical axisrepresents a codeword index.

In FIGS. 11 and 12, R values are I_(VRB) or I_(CCE), which are inone-to-one correspondence with VRB indexes in this embodiment. In FIGS.9 and 11, a value of 0 is I_(offset) and I_(ACK/NACK) can be representedby the sum of R and 0 according to Equations 1 and 2.

As can be seen from these figures, in the case of a first terminal(UE1), I_(ACK/NACK) is 0 since an offset index I_(offset) is 0 andI_(VRB) or I_(CCE) is 0. In the case of UE2, I_(ACK/NACK) is 1 sinceI_(offset) is 0 and I_(VRB) or I_(CCE) is 1. In the case of UE3,I_(ACK/NACK) is 2 since I_(offset) is 1 and I_(VRB) or I_(CCE) is 1.

In the case of remaining UEs 4 to 11, I_(ACK/NACK) can be inferred fromI_(offset) and I_(VRB) or I_(CCE) since I_(offset) and I_(VRB) orI_(CCE) are known.

When a base station transmits an ACK/NACK signal by allocating anACK/NACK index thereto using this method, it is preferable that ACK/NACKindexes not be repeatedly allocated to data transmitted from eachterminal.

It is also preferable that the number of virtual unit resourcesallocated to transmission data be equal to or larger than the rank valueaccording to a MIMO communication scheme applied to the communicationsystem. This is because the number of ACK/NACK resources or indexes thatcan be allocated to a plurality of simultaneously transmitted data canbe easily increased to the number of VRBs or CCEs allocated totransmission data.

For example, when the number of VRBs or CCEs allocated to transmissiondata is 4, using one of the four ACK/NACK indexes is sufficient andtherefore the remaining three can be used for a plurality of data thatare transmitted at the same time. That is, when the number of VRBs orCCEs is 4, it is possible to easily determine ACK/NACK indexes for up tofour simultaneously transmitted data without overlapping of the ACK/NACKindexes.

FIG. 13 illustrates an example where this embodiment of the invention isundesirably applied.

It is preferable that, when a base station performs scheduling,I_(offset) of data be transmitted to prevent ACK/NACK indexes from beingrepeatedly allocated in the same link (uplink or downlink) in the sameframe as described above.

As shown in FIG. 13, when I_(offset) is determined and an ACK/NACK indexis determined according to I_(offset), the same ACK/NACK index may beallocated to different terminals (UEs) so that collisions may occurduring ACK/NACK transmissions.

As can be seen from FIG. 13, in the case of a third terminal (UE3),I_(ACK/NACK) is 5 since I_(offset) is 0 and I_(VRB) or I_(CCE) is 5. Inthe case of UE7, I_(ACK/NACK) is 5 since I_(offset) is 1 and I_(VRB) orI_(CCE) is 4. That is, UE3 and UE7 will transmit ACK/NACK signalsthrough the same ACK/NACK resources since UE3 and UE7 read the sameACK/NACK index. Accordingly, ACK/NACK signals of UE3 and UE7 willcollide.

More specifically, in this method, information of an offset index can betransmitted to a terminal instead of the offset index being directlytransmitted to the terminal. That is, the association is establishedbetween each offset index value and information such as controlinformation, channel information, system information, and terminalinformation for use when data is transmitted from a terminal to provideoffset index information to the terminal so that the terminal can inferan offset index value from the association. Reference will now be madeto a method for determining an offset index value so that it can beinferred in the embodiment in which an offset index is used asadditional information.

First, in an embodiment of the offset index determination method, anoffset index can be determined to be a value corresponding to a pilotsignal. Here, the pilot signal is an un-modulated spread spectrum signalwhich facilitates the terminal to obtain synchronization or base stationinformation. This may be a Reference Signal (RS) according to thecommunication system to which it is applied.

In this case, when data is transmitted in uplink, information OfI_(offset) may be provided to the terminal instead of I_(offset) beingdirectly provided to the terminal. Specifically, an association isestablished between an I_(offset) value and a pilot signal that theterminal will use when transmitting data. The base station notifies theterminal of a pilot signal for use when data is transmitted in uplink toallow the terminal to obtain an I_(offset) corresponding to the pilotsignal.

In a multi-carrier communication system, a set of pilot signals isconstructed so that it is possible to select and use a pilot signal fromthe pilot signal set. Information of the pilot signal set can betransmitted separately. However, a set of pilot signals between thetransmitting and receiving sides, pilot signals included in the pilotsignal set, a pilot signal selected from the pilot signal set, a hoppingrule applied when the pilot signal is selected, or the like can bepreviously defined for use in the system. That is, when the receivingside receives a pilot signal, the receiving side can determine a pilotsignal set and a hopping rule using the pilot signal.

For example, the pilot signal can be constructed as a sequence. Here, itis assumed that a pilot signal to be transmitted together with data isused twice for each data. When a hopping rule wherein pilot signalsequence #1 in a pilot signal set is used at time t=0 and pilot signalsequence #2 is used at time t=1 is applied, pilot signal sequence #1 canbe reused at time t=3 for next data transmission. In the followingdescription, a set of pilot signals that are included in a hopping rangeaccording to the hopping rule applied to a terminal or data in thismanner separately from the pilot signal set will be referred to as apilot signal subset. Thus, the pilot signal set can include a pluralityof pilot signal subsets.

Here, association (or correspondence) is established between an offsetindex value and every sequence that can be used as the pilot signal, andthe offset index can be determined from the association. That is, whenan index assigned to each pilot signal is I_(RS), the offset index canbe determined using I_(RS) such that I_(offset)=I_(RS).

If one or more pilot signals are used when data is transmitted and theone or more pilot signals are variable in a pilot signal set asdescribed above, the offset index value can be determined through thepilot signal set information or the pilot signal subset information.Specifically, the same offset index value may be assigned to the pilotsignal subsets. For example, when an index assigned to a pilot signalsubset that the terminal uses for data transmission is IRS, the offsetindex can be determined such that I_(offset)=I_(RS).

In another method, allocated resource block information other thanI_(RS) can also be used to determine the offset index.

I _(offset) =I _(RS) mod N _(ARB),  EQUATION 3

In Equation 3, I_(offset) denotes an offset index, I_(RS) denotes apilot signal or a pilot signal subset index, and N_(ARB) denotes thenumber of resource blocks or unit resources that the base station hasallocated to the terminal for transmitting and receiving data. Accordingto Equation 3, the pilot signal subset index modulo the number ofresource blocks allocated to the terminal for data transmission isdetermined to be the offset index value. The final ACK/NACK index can bedetermined or inferred using this determined offset index value, forexample by applying it to Equation 1 or 2.

In order to achieve spatial multiplexing of multiple terminals accordingto an MU-MIMO scheme, it is preferable that each terminal use differentpilot signals. To allow each terminal to use a different pilot signal,the base station notifies the terminal of such pilot signal information.For example, the terminal can obtain I_(offset) and ACK/NACK indexinformation using information of a used pilot signal that can beobtained from information of the number of resource blocks N_(ARB)through which data is transmitted and pilot signal subset informationI_(RS) that are transmitted together with the data as described above.

In addition, different pilot signals can be constructed as differentsequences. For example, when a pilot signal sequence is constructed as acombination of a basic sequence of a CAZAC sequence and a cyclic shiftof the basic sequence, the value of offset index I_(offset) can bedetermined taking into consideration a pattern of change with time ofthe cyclic shift or the cyclic shift value.

FIG. 14 illustrates a method of additionally using an offset indexaccording to another embodiment of the invention.

As shown in FIG. 14, a total of 12 VRBs are present on the horizontalaxis and a total of 7 pilot signal subsets available to terminals arepresent on the vertical axis in this embodiment. Here, it is assumedthat multiple pilot signals are used for each data of a terminal (UE)and these pilot signals constitute a pilot signal subset, and an indexis allocated to each pilot signal subset.

Here, a third terminal (UE3) is allocated a total of 4 unit resources(i.e., resource blocks) corresponding to VRB indexes 4 to 9. Likewise,UEs 4, 2, and 5 are each allocated the same VRB resources as those ofUE3. That is, I_(VRB) is 6 and N_(ACK) is 4. Each terminal is allocateda different pilot signal subset. Each terminal can determine an ACK/NACKindex using a VRB index and a pilot signal subset index.

The following is an example where an ACK/NACK index is determined usingEquations 1 and 3. In the case of UE3, an offset index value determinedusing Equation 3 is 0 (=0%4) and thus an ACK/NACK index determined usingEquation 1 is 6. According to the same method, in the case of UE4, theoffset index value is determined to be 2 so that the ACK/NACK index is8. In the case of UE2, the offset index value is determined to be 1 sothat the ACK/NACK index is 7. In the case of UE5, the offset index valueis determined to be 2 so that the ACK/NACK index is 8.

In order to prevent collision of ACK/NACK resources, it is preferablethat at least N VRB resources be allocated to achieve spatialmultiplexing of N terminals. In this embodiment, the pilot signal subsetindex modulo the number of resource blocks allocated to terminal data isdetermined to be the offset index value. Therefore, it is preferablethat the base station perform scheduling such that the offset indexvalue obtained for each user through the modulo operation is unique.

In the embodiment illustrated in FIG. 14, the system can be operatedwithout collision of ACK/NACK resources by using ACK/NACK indexes 6, 8,and 7 for UE3, UE4, and UE2, respectively. However, even though UE3 andUE5 use different pilot signal subsets, their offset values obtainedthrough the modulo operation are equal so that their ACK/NACK indexesare identical. Therefore, if scheduling is performed in this manner,collision is expected to occur between ACK/NACK resources of UE3 andUE5.

Another embodiment of the invention is that pilot signals or pilotsignal subsets are grouped into one or more groups and information ofthe pilot signal groups is used. For example, pilot signal subsets orpilot signals in a pilot signal set are divided into N_(RSG) groups andan index is allocated to each divided group so that it can be used todetermine an offset index or an ACK/NACK index. The number of pilotsignal groups may be one or more and such pilot signal group informationcan be transmitted to a terminal.

Equations 4 and 5 illustrate examples where an offset index isdetermined using pilot signal group information.

I _(dffset) =I _(RS) mod N _(ARB) +I _(RSG)  EQUATION 4

I _(dffset) =I _(RS) mod N _(ARB) +G(I _(RS))  EQUATION 5

Similar to Equation 3, I_(offset) and I_(RS) in Equations 4 and 5 denotean offset index and a pilot signal or a pilot signal subset index,respectively, and N_(ARB) denotes the number of resource blocks or unitresources that the base station has allocated to the terminal fortransmitting and receiving data. I_(RSG) denotes an index of the pilotsignal group described above.

In Equation 5, G( ) is a function for determining a pilot signal groupindex. For example, pilot signal group index information can bedetermined from a pilot signal or pilot signal subset index, where G( )is a function for inferring a pilot signal group index from the pilotsignal or pilot signal subset index.

As a specific embodiment, let us assume that a total of 8 pilot signalsubsets are included in a pilot signal set and are grouped into pilotsignal groups, each including 4 pilot signal subsets. In this case, thepilot signal subsets are grouped into a total of 2 pilot signal groups.When the number of ACK/NACK resources is twice the number of VRBs, anindex I_(RSG) of one of the pilot signal groups can be determined to be0 and an index of the other pilot signal group can be determined to beequal to the total number of VRBs. In this manner, a larger number ofACK/NACK resources than the number of VRBs can be determined in thesystem.

FIG. 15 illustrates a method of additionally using an offset indexaccording to another embodiment of the invention.

As shown in FIG. 15, similar to the embodiment of FIG. 14, a total of 12VRBs are present on the horizontal axis and a total of 7 pilot signalsubsets available to terminals are present on the vertical axis in thisembodiment. Here, it is assumed that multiple pilot signals are used foreach data of a terminal (UE) and these pilot signals constitute a pilotsignal subset, and an index is allocated to each pilot signal subset.

In the case of FIG. 15, it is also assumed that a total of 7 pilotsignal subsets are grouped into two pilot signal groups, and the firstpilot signal group (RS Group 1) includes four pilot signal subsets ofpilot signal subset indexes 0 to 3 and the second pilot signal group (RSGroup 2) includes three pilot signal subsets of pilot signal subsetindexes 4 to 6. In this case, 0 and 12, which is the total number ofVRBs, can be allocated to the first pilot signal group and the secondpilot signal group, respectively. That is, as shown in FIG. 15, thepilot signal group index of the first pilot signal group is determinedto be 0, and the pilot signal group index of the second pilot signalgroup is determined to be 12.

Here, a third terminal (UE3) is allocated a total of 3 unit resources(i.e., resource blocks) corresponding to VRB indexes 6 to 8. Likewise,UEs 4, 2, and 5 are each allocated the same VRB resources as those ofUE3. That is, I_(VRB) is 6 and N_(ACK) is 3. Each terminal is allocateda different pilot signal subset. Each terminal can determine an ACK/NACKindex using a VRB index, a pilot signal subset index, and the pilotsignal group index described above.

The following is an example where an ACK/NACK index is determined usingEquations 1 and 4. In the case of UE3, an offset index value determinedusing Equation 4 is 0 (=0%4+0) and thus an ACK/NACK index determinedusing Equation 1 is 6. According to the same method, in the case of UE2,the offset index value is determined to be 1 so that the ACK/NACK indexis 7. In the case of UE4, the offset index value is determined to be 2so that the ACK/NACK index is 8. In the case of UE5, the offset indexvalue is determined to be 12 (=6%3+12) so that the ACK/NACK index is 18.In order to allow the base station to receive a plurality of codewordstransmitted from one or more terminals in uplink that are multiplexed inthe same time-frequency region, it should be possible for the basestation to obtain channel information of a plurality of antennas orterminals. Pilot signals can be used to notify the base station ofchannel information of the antennas or terminals. It is preferable thatpilot signals be orthogonal to each other or that pilot signals havegood cross-correlation characteristics. Therefore, when a terminaltransmits data in uplink using a MIMO technique, the terminal informsthe base station of a pilot signal to be used before transmitting thedata.

Accordingly, this embodiment suggests a method of using a relation thatis established between pilot signals, which multiple terminals use inthe frequency domain through which data is transmitted, and offsetindexes that affect the determination of ACK/NACK indexes. Since thepilot signal value is different for each terminal or antenna asdescribed above, it will be effective to use the pilot signal value forthe offset index value. For example, when a number is assigned to apilot signal allocated to each terminal or antenna, its value can bedetermined to be I_(offset).

In another embodiment of the offset index determination method, theoffset index can be determined to be a value corresponding toinformation of a codeword corresponding to data transmitted throughmultiple antennas using the same time-frequency resources.

When data is transmitted according to an SU-MIMO scheme, information ofa precoding matrix used for the data transmission is provided.Accordingly, the terminal can infer a codeword index of each datacodeword through the used precoding matrix information and the codewordindex can be used as an offset index. In this case, the base station candetermine an I_(offset) value from the codeword index without separatelytransmitting I_(offset) to the terminal.

In downlink MU-MIMO, the terminal can at least determine a column vectorin the precoding matrix that has been used for data transmission. Thatis, when a precoding matrix used by both the base station and theterminal has been predetermined, it is possible to determine the ordinalnumber of the column vector in the precoding matrix. Accordingly, it ispossible to infer a codeword index of each data codeword and to use thecodeword index as the offset index. Similar to the case of SU-MIMO, inthis case, the base station can determine an I_(offset) value from thecodeword index without separately transmitting I_(offset) to theterminal.

In this embodiment, in the case where an ACK/NACK index is determinedusing a codeword in a system which transmits data using a MIMOtechnique, the base station transmits a signal corresponding to theordinal number of a codeword as control information when the basestation allocates data to the terminal, thereby allowing the terminal toobtain a codeword index of each data.

If a precoding matrix used in the MIMO scheme is known to both the basestation and the terminal and a relation is fixedly established betweencodewords and layers, the order of codewords corresponding respectivelyto a plurality of data can be determined to be the same as the order ofcodeword column vectors. That is, in the case where a codeword isprecoded according to the MIMO technique and is transmitted through anactual physical transmit antenna, the codeword index may indicate theordinal number of a column vector of data symbols before the codeword ismapped to a layer.

If the terminal does not know a precoding matrix used in the basestation and instead knows a precoding column vector which is a part ofthe precoding matrix, the base station notifies the terminal of theordinal number of the precoding column vector in the precoding matrix orof the codeword index of corresponding data, thereby allowing theterminal to transmit an ACK/NACK signal for the corresponding data.

In addition, if it is possible to determine the ordinal number of theprecoding column vector applied to the data in the precoding matrix, itis possible to determine the ordinal number of a layer corresponding tothe data. Then, it is possible to determine the ordinal number of acodeword corresponding to the data based on the predetermined relationbetween codewords and layers, thereby obtaining the codeword index.

Reference will now be made to a method in which an ACK/NACK index isdetermined using a combination of a VRB index and a codeword indexaccording to another embodiment of the invention.

In the following, it is assumed that a relation is fixed betweencodewords and layers in a multi-carrier MIMO system. Equation 6illustrates an example of the ACK/NACK index determination method whichcan be applied under this assumption.

I _(ACK/NACK) =α·I _(Codeword) +β·I _(VRB)  EQUATION 6

In Equation 6, I_(ACK/NACK) is an ACK/NACK index which is a uniquenumber indicating a physical resource through which each availableACK/NACK signal may be transmitted or received, I_(Codeword) is acodeword index which is a number allocated to each codeword fortransmitting data, and I_(VRB) is a number corresponding to a VRB thatis selected according to a specific rule from a set of VRBs throughwhich data corresponding to a codeword is transmitted when it is assumedthat VRB indexes are numbers allocated to all VRBs through which data istransmittable. For example, I_(VRB) may be the smallest VRB index amongVRB indexes corresponding to VRBs occupied by data corresponding to acodeword, i.e., among VRB indexes corresponding to VRBs through whichthe data corresponding to the codeword can be transmitted. In addition,α and β are constants.

More specifically, in this embodiment, the number of resources allocatedfor ACK/NACK transmission is N_(codeword) times the VRB index and up toN_(codeword) codewords can be transmitted in the same time-frequencyregion. When the number of VRB indexes I_(VRB) is N_(VRB), the ACK/NACKindex can be determined using the following Equation 7 or 8.

I _(ACK/NACK) =N _(VRB) ·I _(Codeword) +I _(VRB) , I _(Codeword)=0,1,2,. . . ,N _(Codeword)−1, I _(VRB)=0,1,2, . . . ,N _(VRB)−1  EQUATION 7

I _(ACK/NACK) =I _(Codeword) +N _(codeword) ·I _(VRB) , I_(Codeword)=0,1,2, . . . ,N _(Codeword)−1, I _(VRB)=0,1,2, . . . ,N_(VRB)−1  EQUATION 8

In Equations 6 to 8, I_(VRB) is not necessarily in one-to-onecorrespondence with VRB indexes.

In addition, when data of one codeword transmitted using MIMO istransmitted in units of sets of at least M VRBs, I_(VRB) may be inone-to-one correspondence with the set of VRBs. That is, if data isallocated to VRBs in units of sets of two VRBs in a MIMO system in whichup to two codewords can be transmitted, one I_(VRB) number is allocatedto each set of two VRBs and an ACK/NACK index of an ACK/NACK resourcefor use by data of each codeword can be determined using I_(codeword)which is a number indicating the codeword.

Reference will now be made to a method in which an ACK/NACK index isdetermined using a combination of a CCE index and a codeword indexaccording to another embodiment of the invention.

In the following, it is assumed that a relation is fixed betweencodewords and layers in a multi-carrier MIMO system. Equation 9illustrates an example of the ACK/NACK index determination method whichcan be applied under this assumption.

I _(ACK/NACK) =α·I _(Codeword) +βI _(CCE)  EQUATION 9

In Equation 9, I_(ACK/NACK), I_(Codeword), and I_(CCE) are an ACK/NACKindex, a codeword index, and a CCE index, respectively. Particularly,I_(CCE) may correspond to a CCE included in a set of one or more CCEsoccupied by control information indicating a physical resource positionof transmission data. When control information is transmitted through aplurality of CCEs, I_(CCE) may be a number corresponding to an index ofa CCE that is selected from the plurality of CCEs according to aspecific rule. For example, I_(CCE) may be the smallest CCE index amongCCE indexes corresponding to one or more CCEs occupied by single controlinformation. Similar to Equation 6, α and β in Equation 9 may constants.

Similar to the case where VRB indexes are used, in this embodiment, thenumber of resources allocated for ACK/NACK transmission is N_(codeword)times the CCE index and up to N_(codeword) codewords can be transmittedin the same time-frequency region. When the number of CCE indexesI_(CCE) is N_(CCE), the ACK/NACK index can be determined using thefollowing Equation 10 or 11.

I _(ACK/NACK) =N _(CCE) ·I _(Codeword) +I _(CCE) , I _(Codeword)=0,1,2,. . . ,N _(Codeword)−1, I _(CCE)=0,1,2, . . . ,N _(CCE)−1  EQUATION 10

I _(ACK/NACK) =I _(Codeword) +N _(codeword) ·I _(CCE) , I_(Codeword)=0,1,2, . . . ,N _(Codeword)−1, I _(CCE)=0,1,2, . . . ,N_(VRB)−1  EQUATION 11

A description of Equations 10 and 11 is omitted here since it is similarto the description of Equations 6 to 8.

In another embodiment of the invention, the additional informationdescribed above can be changed according to at least one of a virtualunit resource allocated to the transmission data and a virtual unitresource allocated to control information of the transmission data.

For example, an ACK/NACK index can be obtained by analyzing theI_(offset) value, which is one example of the additional information,differently according to a VRB index of a VRB through which data wastransmitted. This can be represented by Equation 12 as follows.

I _(ACK/NACK) =O(I _(offset))+I _(VRB) , I _(VRB)=0,1,2, . . . N_(VRB)−1  EQUATION 12

In Equation 12, 0( ) can be considered a function for analyzing theI_(offset) value differently according to a VRB index of a VRB throughwhich data was transmitted. The function 0( ) can be predetermined byboth the base station and the terminal.

For example, the smallest of an array of VRB indexes of all VRBsoccupied by data transmitted according to codewords is subtracted fromeach of the VRB indexes. Each VRB index included in the array ofsubtracted VRB indexes is referred to as a VRB differential index. Inaddition, it is assumed that a codeword index is used as an I_(offset)value. Here, an input of the function 0( ) may be a value indicating theordinal number of the VRB differential index in the array and an outputof the function 0( ) may be a value indicated by the input among thevalues of the VRB differential index in the array. Here, similar to theabove embodiments, I_(VRB) represents the smallest of the VRB indexes ofVRBs through which codewords were transmitted.

Even when multiple codewords are transmitted through the samefrequency-time region using the MIMO scheme, the amount of ACK/NACKresources required for this will not be increased compared to when noMIMO scheme is applied if the number of VRBs through whichMIMO-multiplexed codewords are transmitted is limited so that it isalways larger than a rank value applied to MIMO multiplexing.

Here, the I_(offset) value can naturally be determined using a varietyof methods including not only the method of using a codeword indexdescribed above but also the method of using a pilot signal describedabove with reference to Equations 3 to 5.

An embodiment in which offset index values are changed according to VRBindexes will now be described with reference to FIGS. 16 and 17.

FIG. 16 illustrates an example of the ACK/NACK index determinationmethod according to another embodiment of the invention.

In the example of FIG. 16, it is assumed that one codeword istransmitted to each different terminal and each codeword is transmittedthrough VRB indexes 2, 4, 5, and 7 and the offset index is identical tothe codeword index. Here, the I_(VRB) value of every terminal is 2.

It is also assumed that 0( ) is a function that outputs a valuecorresponding to a VRB differential index as described above. First, thesmallest VRB index 2 is subtracted from the VRB indexes 2, 4, 5, and 7to calculate VRB differential indexes. The calculated VRB differentialindexes are 0, 2, 3, and 5. Thus, 0(I_(offset)) is 0 if the offset indexvalue is 0, 2 if the offset index value is 1, 3 if the offset indexvalue is 2, and 5 if the offset index value is 3.

With reference to Equation 12, the ACK/NACK index of UE1 is determinedto be 7 (=5+2), the ACK/NACK index of UE2 is determined to be 5 (=3+2),the ACK/NACK index of UE3 is determined to be 4 (=2+2), and the ACK/NACKindex of UE4 is determined to be 2 (=0+2).

FIG. 17 illustrates an example of the ACK/NACK index determinationmethod according to another embodiment of the invention.

In the example of FIG. 17, it is assumed that two codewords aretransmitted to different terminals, and data is transmitted to UE1through VRB indexes 2, 5, and 7 and data is transmitted to UE2 throughVRB indexes 3 and 8. It is also assumed that the offset index isidentical to the codeword index. Here, the I_(VRB) value of UE1 is 2 andthe I_(VRB) value of UE2 is 3.

It is also assumed that 0( ) is a function that outputs a valuecorresponding to a VRB differential index as described above. First, thesmallest VRB index 2 is subtracted from the VRB indexes 2, 5, and 7 ofUE1 to calculate VRB differential indexes. The calculated VRBdifferential indexes are 0, 3, and 5. Likewise, the smallest VRB index 3is subtracted from the VRB indexes 3 and 8 of UE2 to calculate VRBdifferential indexes. The calculated VRB differential indexes are 0 and5.

With reference to Equation 12, in the case of UE1, an ACK/NACK indexcorresponding to data corresponding to the codeword index 0 isdetermined to be 2 (=0+2) and an ACK/NACK index corresponding to datacorresponding to the codeword index 1 is determined to be 5 (=3+2). Inthe case of UE2, an ACK/NACK index corresponding to data correspondingto the codeword index 0 is determined to be 3 (=0+3) and an ACK/NACKindex corresponding to data corresponding to the codeword index 1 isdetermined to be 8 (=5+3).

The above embodiments of the present disclosure have been describedfocusing on the data communication relationship between a terminal (UE)and a base station. The base station is a terminal node in a networkwhich performs communication directly with the terminal. Specificoperations which have been described as being performed by the basestation may also be performed by upper nodes as needed. That is, it willbe apparent to those skilled in the art that the base station or anyother network node may perform various operations for communication withterminals in a network including a number of network nodes. The term“base station” may be replaced with another term such as “fixedstation”, “Node B”, “eNode B (eNB)”, or “aCCEss point”. The term“terminal” may also be replaced with another term such as “userequipment (UE)”, “mobile station (MS)”, “mobile station (MS)”, or“mobile subscriber station (MSS)”.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific forms than those set forth herein withoutdeparting from the spirit and essential characteristics of the presentinvention. The above description is therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by reasonable interpretation of the appended claimsand all changes coming within the equivalency range of the invention areintended to be embraced in the scope of the invention.

INDUSTRIAL APPLICABILITY

The present invention can be applied to mobile communication systems,cellular mobile communication systems, cellular multi-carrier systems,etc.

1-11. (canceled)
 12. A method for receiving by a user equipmentacknowledgement/Negative ACK (ACK/NACK) signals from a network node in amultiple input multiple output (MIMO) mobile communication system, themethod comprising: transmitting, to the network node, a plurality ofdata blocks by using one or more physical resource blocks (PRBs),wherein the data blocks are converted into respective codewords mappedto layers for MIMO transmission, and each PRB is one-to-one mapped to arespective virtual resource block (VRB); and receiving, from the networknode, ACK/NACK signals of the plurality of data blocks, wherein aresource index for the ACK/NACK signal corresponding to a first datablock of the plurality of data blocks is identified by using β×I_(RB),wherein a resource index for the ACK/NACK signal corresponding to asecond data block of the plurality of data blocks is identified by usingα+β×I_(RB), wherein α is a constant, β is a constant, and I_(RB) is alowest PRB index of one or more PRB indexes corresponding to the one ormore PRBs.
 13. The method of claim 12, wherein α is a constant otherthan
 0. 14. The method of claim 13, wherein α is a positive integer. 15.The method of claim 13, wherein β is a constant other than
 0. 16. Themethod of claim 12, further comprising: receiving, from the networknode, uplink resource allocation for the plurality of data blocks.
 17. Amethod for transmitting by a network node acknowledgement/Negative ACK(ACK/NACK) signals to a user equipment in a multiple input multipleoutput (MIMO) mobile communication system, the method comprising:receiving, from the user equipment, a plurality of data blocks by usingone or more physical resource blocks (PRBs), wherein the data blocks areassociated with respective codewords mapped to layers for MIMOtransmission, and each PRB is one-to-one mapped to a respective virtualresource block (VRB); and transmitting, to the user equipment, ACK/NACKsignals of the plurality of data blocks, wherein a resource index forthe ACK/NACK signal corresponding to a first data block of the pluralityof data blocks is identified by using β×IRB, wherein a resource indexfor the ACK/NACK signal corresponding to a second data block of theplurality of data blocks is identified by using α+β×IRB, wherein α is aconstant, β is a constant, and IRB is a lowest PRB index of one or morePRB indexes corresponding to the one or more PRBs.
 18. The method ofclaim 17, wherein α is a constant other than
 0. 19. The method of claim18, wherein α is a positive integer.
 20. The method of claim 18, whereinβ is a constant other than
 0. 21. The method of claim 17, furthercomprising: transmitting, to the user equipment, uplink resourceallocation for the plurality of data blocks.
 22. A user equipment usedfor receiving acknowledgement/Negative ACK (ACK/NACK) signals from anetwork node in a multiple input multiple output (MIMO) mobilecommunication system, the user equipment comprising: a memory unit; anda processor, wherein the processor is configured to: transmit, to thenetwork node, a plurality of data blocks by using one or more physicalresource blocks (PRBs), wherein the data blocks are converted intorespective codewords mapped to layers for MIMO transmission, and eachPRB is one-to-one mapped to a respective virtual resource block (VRB);and receive, from the network node, ACK/NACK signals of the plurality ofdata blocks, wherein a resource index for the ACK/NACK signalcorresponding to a first data block of the plurality of data blocks isidentified by using β×I_(RB), wherein a resource index for the ACK/NACKsignal corresponding to a second data block of the plurality of datablocks is identified by using α+β×I_(RB), wherein α is a constant, β isa constant, and I_(RB) is a lowest PRB index of one or more PRB indexescorresponding to the one or more PRBs.
 23. The user equipment of claim22, wherein α is a constant other than
 0. 24. The user equipment ofclaim 23, wherein α is a positive integer.
 25. The user equipment ofclaim 23, wherein β is a constant other than
 0. 26. The user equipmentof claim 22, wherein the processor is further configured to: receive,from the network node, uplink resource allocation for the plurality ofdata blocks.
 27. A network node used for transmittingacknowledgement/Negative ACK (ACK/NACK) signals to a user equipment in amultiple input multiple output (MIMO) mobile communication system, thenetwork node comprising: a memory unit; and a processor, wherein theprocessor is configured to: receive, from the user equipment, aplurality of data blocks by using one or more physical resource blocks(PRBs), wherein the data blocks are associated with respective codewordsmapped to layers for MIMO transmission, and each PRB is one-to-onemapped to a respective virtual resource block (VRB); and transmit, tothe user equipment, ACK/NACK signals of the plurality of data blocks,wherein a resource index for the ACK/NACK signal corresponding to afirst data block of the plurality of data blocks is identified by usingβ×IRB, wherein a resource index for the ACK/NACK signal corresponding toa second data block of the plurality of data blocks is identified byusing α+β×IRB, wherein α is a constant, β is a constant, and IRB is alowest PRB index of one or more PRB indexes corresponding to the one ormore PRBs.
 28. The network node of claim 27, wherein α is a constantother than
 0. 29. The network node of claim 28, wherein α is a positiveinteger.
 30. The network node of claim 28, wherein β is a constant otherthan
 0. 31. The network node of claim 27, wherein the processor isfurther configured to: transmit, to the user equipment, uplink resourceallocation for the plurality of data blocks.